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Thin rope!
We have been discussing on our team how a thin rope will be attached on the air ship. With a thick rope its the knot that keeps it from sliding through the two tabs with the pin through it. If you use a thin rope, do you have to make a really big knot? Or can you make a loop and hook it to something? Anybody out there know? Thanks in advance!
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You are required to have a retaining feature greater than 1 inch in your rope.
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Take a look at the monkeys fist knot. It's pretty large and depending on the number of windings you do, can be as large as you'd like. Also they look really cool!
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It looks like a Slot that the knot sits in, so if you have a thin rope, with a thin knot, it will slip through.
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Something like this? http://www.sky-international.com/pro...e-ball-fenders
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Just realized those things are huge. Some shaped like that would work. Maybe a disc swing could be used as the top anchor? Or would that be too big?
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We're looking at a .301" diameter rope a that should spool very nicely, but I'm afraid of looking back and thinking we could've done more.
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![]() The image above is a three-strand monkey's fist in 3/8" braided polyester rope. Knot diameter ~2.3 inch. Rep points to the first student who ties one, measures the length of rope required between the two taped points, and posts a correct result (+/- 30 mm). |
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I was under the assumption that the retaining feature could be a loop and/or knot. Because the davit has 2 steel fingers, with the manual saying:
These fingers are 1¼ in. (~3 cm) apart and have a hole for a locking pin. The ROPE passes through the fingers with the top knot on the AIRSHIP side of the fingers. This phrasing implies that there has to be a knot, because the top knot is on the AIRSHIP side of the fingers, but part of me thinks this only is referring to the rope installed on the field. But the definition of ROPE, seems to imply otherwise. However, the black rope in the picture in IO4 has 2 loops: ![]() and IO4 E says: E. be configured such that it engages securely with the FIELD. To interface with the field a ROPE must have a retaining feature (e.g. a knot) greater than 1 in. (~25.4 mm) in diameter to interface with the DAVITS (RF). This seems to say something other than a knot is allowed. There seems to be contradicting info, but if a loop is allowed it seems like you could just put a loop around one of the steel fingers on the davit and it would still pass through the fingers |
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Frankly, from a safety standpoint, I'm surprised a 100% safe method for securing the rope at the top isn't being required. If a team uses a thin rope with a knot they presume is thick enough but isn't under certain scenarios (e.g. hanging robot actually bumped by another robot), then the hanging robot could fall to the ground with the current guidelines. A worse scenario would be the robot falling on a person because the top knot slipped through the 1" opening after the match when students are trying to extract their robot. There are many types of rope/cord out there with different characteristics. It would have been far safer IMO to include in the KoP a 100% reliable plastic anchor compatible with any (within reason) type of rope OR to require a loop at the top and usage of the fingers mentioned in the previous post.
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Personally I'm surprised that the GDC hasn't implemented a minimum width for this exact reason. Maximum 1", minimum 0.5", for example. |
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